The disclosure of the commonly owned pending German priority application Serial No. 199 50 082.7 (filed Oct. 18, 1999), as well as of each U.S. and foreign patent and patent application identified in the specification of the present application, is incorporated herein by reference.
This invention relates to pumps in general, and more particularly to improvements in hydraulic pumps of the type known as master cylinders. Such master cylinders are utilized in many types of motor vehicles to actuate clutches and/or brakes.
A master cylinder normally comprises a cylindrical housing, a piston which is reciprocable in and defines with the housing a plenum chamber for a supply of hydraulic fluid, a piston rod or push rod which can receive motion from a pedal or from an actuator to shift the piston from a retracted position to an extended position and to thus pressurize and expel pressurized fluid into the cylinders of the brake system or into the cylinder of the clutch actuating mechanism, and at least one spring serving to cause the piston to reassume its retracted position when the operator of the motor vehicle ceases to depress the brake pedal or the clutch pedal or when the operation of the brake or clutch is interrupted by the actuator which receives signals from the control unit for the power train of the motor vehicle.
Published German patent application Serial No. 197 55 548 discloses a master cylinder wherein the piston is movable axially relative to two spaced-apart sealing rings which are sealingly installed in the housing and sealingly engage the piston. A drawback of such master cylinders is that each actuation can involve, or is likely to involve, the generation of often highly pronounced and highly unpleasant screeching, creaking or squealing noises attributable to the absence of any or adequate films of lubricant between the parts (such as the piston and the sealing rings) which must move relative to each other in response to depression of the brake pedal or clutch pedal. Thus, the adhesion between the surface of the piston and the surface(s) of one or more sealing elements is likely to be sufficiently pronounced to cause the generation of readily detectable noise whenever the operator of the motor vehicle decides to move the piston relative to the housing of the master cylinder or when such decision is rendered by the electronic control unit and effected by the actuator of the prime mover in the motor vehicle.
The generation of the just discussed noise can be avoided, or the intensity of such noise can be reduced, by adequate lubrication, i.e., by the establishment of a satisfactory hydrodynamic film of lubricant between the surface or surfaces of the moving part(s) (such as the piston) and the stationary part(s), such as the housing and/or the sealing element(s) of the master cylinder. It has been ascertained that a master cylinder is likely to generate noise regardless of whether its piston is made of steel, aluminum or a plastic material with or without a metallic or plastic jacket. The generation of noise is attributable to the development of oscillations which can or are likely to be sufficiently pronounced to constitute a cause of discomfort to the operator and other occupant(s) of the motor vehicle.
Attempts to overcome such drawbacks of presently known master cylinders by utilizing special lubricants have met with limited success, partly or mainly because it is difficult or impossible to ensure adequate lubrication during the entire useful life of the master cylinder and/or of the arrangement (such as the brake system or the clutch) which is connected with and is actuated by the master cylinder.
Another drawback of many presently known master cylinders is that they are likely to be vibrated by the parts which receive pressurized fluid from the plenum chamber of the housing. For example, if the master cylinder is installed to actuate the disengaging unit (such as a slave cylinder) for a friction clutch in the power train of a motor vehicle, vibrations of the slave cylinder (such vibrations are normally attributable to vibrations of the internal combustion engine in the power train) are a cause of pulsating changes of fluid pressure in the conduit connecting the slave cylinder with the chamber in the housing of the master cylinder. The fluid (such as oil) in the chamber of the housing causes the piston of the master cylinder to vibrate and to transmit such undesirable movements to the piston rod and thence to the clutch pedal or to the actuator, depending upon the nature of the clutch (i.e., whether the clutch is disengaged in response to actuation of a pedal or in response to signals furnished to the actuator by an electronic control circuit). The just discussed oscillations of the piston rod are a cause of discomfort and/or uncertainty to the operator of the motor vehicle and/or a cause of undesirable stressing of the actuator for the clutch.
A power train wherein the clutch is actuated by a master cylinder by way of a slave cylinder is disclosed, for example, in commonly owned U.S. Pat. No. 5,632,706 granted May 27, 1997 to Kremmling et al. for xe2x80x9cMOTOR VEHICLE WITH ELECTRONIC CLUTCH MANAGEMENT SYSTEMxe2x80x9d.
An object of the invention is to provide a single or dual master cylinder which is constructed and assembled in such a way that movements of its piston(s) relative to the housing(s) are less likely to generate pronounced noise (or any noise) than the movements of the piston(s) in conventional master cylinders for use in the power trains of motor vehicles.
Another object of the invention is to provide a master cylinder the operation of which is satisfactory (such as without the generation of any noise or any appreciable noise) during the entire useful life of the master cylinder and/or of the power train in which the master cylinder is put to use.
A further object of the invention is to provide a master cylinder which is constructed and assembled in such a way that it prevents the transmission of undesirable stray movements from one or more controlled parts (such as a slave cylinder) to the part or parts (such as a pedal or an actuator) serving to actuate the master cylinder.
An additional object of the invention is to provide a simple, inexpensive and reliable solution of the aforediscussed problems associated with the utilization of conventional single or dual master cylinders.
Still another object of the invention is to provide a novel housing-piston combination for use in the above outlined master cylinder.
A further object of the invention is to provide a novel and improved housing-seal-piston combination for use in the improved master cylinder.
Another object of the invention is to provide a novel and improved piston-piston rod combination for use in the above outlined master cylinder.
An additional object of the invention is to provide a novel and improved piston for use in the master cylinder.
Still another object of the invention is to provide a novel and improved method of preventing the generation of noise (or pronounced noise) during actuation of a master cylinder in the power train of a motor vehicle.
A further object of the instant invention is to provide a novel and improved method of preventing the transmission of stray movements from a slave cylinder or from a combustion engine to the piston rod or to the actuator which is utilized to initiate the operation of the improved master cylinder.
Another object of the invention is to provide a motor vehicle wherein the power train employs one or more novel and improved master cylinders.
An additional object of the invention is to provide a novel and improved brake system for use in a motor vehicle.
Still another object of the invention is to provide a novel and improved friction clutch assembly for use in a motor vehicle.
A further object of the present invention is to provide novel and improved methods of making pistons for use in master cylinders for the brakes or clutches of motor vehicles.
Another object of the invention is to provide a novel and improved conduit for use in or in conjunction with the above outlined master cylinder.
One feature of the present invention resides in the provision of a master cylinder which can be utilized in a motor vehicle and comprises a housing, a piston member which is coaxial with and is movable axially within and defines with the housing a variable-volume chamber, means (such as a piston rod) for moving the piston axially of the housing, at least one sealing member (e.g., an annular seal) interposed between the piston member and the housing, and means for turning the piston member and/or the at least one sealing member relative to the other of these members in response to axial movement of the piston member relative to the housing.
As already mentioned above, the means for moving the piston member relative to the housing can comprise a piston rod, and such piston rod can receive motion from a brake actuating device (such as a pedal) or a clutch actuating device (such as a pedal or an actuator). The piston member is disposed in the housing between the chamber and the piston rod. The latter can be connected with the piston member by a suitable swivel joint, e.g., a cardan joint or another universal joint.
If the sealing member(s) is(are) non-rotatably installed in the housing, the means for turning includes means for rotating the piston member relative to the housing. Such rotating means can comprise at least one at least partially helical internal groove in the housing and at least one follower (e.g., a tooth or an analogous projection) provided on the piston member and being confined in the at least one groove. The piston member can comprise a jacket and a core in the jacket, and the at least one follower can be provided on the core and/or on the jacket.
Broadly stated, the means for turning can comprise an internal thread provided in one of the housing and the piston member, and a complementary external thread mating with the internal thread and provided on the other of the housing and the piston member. The aforementioned projection can be considered or interpreted as constituting a rudimentary thread.
In accordance with one presently preferred embodiment, the means for turning can comprise an internal thread which is provided in the piston member and an external thread provided on a stem (e.g., a part analogous to the stem of an externally threaded bolt) carried by the housing and mating with the internal thread. The means for moving can comprise a piston rod. The piston member of such master cylinder is or can be provided with a first end portion which is connected to the piston rod and a second end portion at the chamber; the internal thread can be provided in an axial bore or hole made in the piston member and extending from its second end portion toward the first end portion, and the stem includes a portion which extends into the hole or bore of the piston member.
The means for turning can further comprise resilient means which reacts against the housing to bear upon the piston member or vice versa and to thus bias the piston member axially of the housing. Such resilient means can serve, or can also serve, to return the piston member from its extended to its starting or retracted position.
The resilient means can include or constitute a bistable spring.
The piston member may but need not be hollow and can be made, at least in part, of a plastic material; such piston member or such part of the piston member can constitute an injection molded article.
The piston member can be constructed and assembled in such a way that it includes an outer portion which is adjacent the internal surface of the housing and means for reinforcing the outer portion of such piston member; for example, the reinforcing means can include or constitute at least one internal brace in the interior of the piston member.
A thrust bearing can be interposed between the piston member and the piston rod; in such master cylinders, that portion of the piston member which is adjacent the bearing has a hardness less than that of the adjacent portion of the bearing.
In accordance with another embodiment of the present invention, the improved master cylinder comprises a housing, a piston member (hereinafter called piston) which is coaxial with and is reciprocable within and defines with the housing a variable-volume chamber for a supply of oil or another suitable hydraulic fluid, means (e.g., including a piston rod) for moving the piston relative to the housing, and at least one sealing member which is interposed between the piston and the housing. The piston has a specially designed or finished surface (hereinafter called patterned surface) which contacts the at least one sealing member and is configured, finished and/or otherwise patterned in a manner to reduce the likelihood of adherence of the piston to the sealing member or members. Such patterned surface can reduce or eliminate the tendency of the piston and the sealing member or members to generate noise in response to movement of the piston and of the housing relative to each other.
At least that portion of the piston which is adjacent to its patterned surface can consist of a plastic material; such portion of the piston can constitute an injection molded article. Alternatively, at least that portion of the piston which is adjacent to its patterned surface can consist of a suitable metallic material.
The piston can include a core and a layer which surrounds at least a portion of the core. At least a portion of the patterned surface can be provided on such layer, and the layer can be made of a plastic material such as a fluorocarbon resin, e.g., polytetrafluorethylene, polyvinylidene fluoride or fluorinated ethylene propylene.
Alternatively, the layer can consist of a mixture of metallic and plastic materials; such mixture can contain nickel and/or polytetrafluorethylene. The mixture can contain between about 5 and 30 percent by weight of plastic material, preferably between about 10 and 15 percent.
It is also possible to make the aforementioned layer of the piston of amorphous carbon; such layer can have a thickness of between about 1 and 10 xcexcm.
The layer can be applied to the core of the piston in accordance with the zinc phosphating process, and such layer can have a thickness of between about 2 and 7 xcexcm.
Regardless of its composition, a presently preferred thickness of the layer is in the range of between about 1 and 50 xcexcm, more preferably between about 2 and 15 xcexcm and most preferably between about 5 and 10 xcexcm.
The patterned surface of the piston can be a roughened surface; alternatively, it can exhibit a substantially rhombic, a substantially circular or a substantially polygonal pattern.
Furthermore, the patterned surface can be provided with recesses having a depth in the range of up to 5 xcexcm, preferably of up to 1 xcexcm.
Still further, the patterned surface can be defined by a plurality of minute segments each of which has a length and/or width within a range of up to about 1 mm, preferably within a range of between about 1 and 100 xcexcm.
The means for moving can comprise resilient means reacting against the piston or against the housing and bearing upon the housing or the piston to bias the piston axially of the housing; such resilient means can comprise at least one bistable spring.
The piston can be hollow, and at least a portion of the (hollow or solid) piston can consist of a plastic material; for example, the plastic portion of the piston can constitute an injection molded article.
That (outer) portion of the piston which is adjacent the patterned surface can be reinforced, e.g., by one or more internal braces.
If the means for moving the piston comprises or constitutes a piston rod, the improved master cylinder can further embody a thrust bearing which is interposed between the piston and the piston rod. That portion of the piston which is adjacent the thrust bearing exhibits a first hardness, and that portion of the thrust bearing which is adjacent the just mentioned portion of the piston can have a second hardness different from and normally greater than the first hardness.
A further feature of the present invention resides in the provision of a master cylinder which can be utilized in motor vehicles and comprises a housing, a piston which is coaxial with and has an external surface in the housing, means for moving the piston relative to the housing including a piston rod which is connected with one end portion of the piston, and means for damping vibrations in the power train between the piston rod and the external surface of the piston. The other end portion of the piston and the housing define a variable-volume chamber.
The piston can further comprise a core including the one end portion of the piston, and a jacket for the core. The aforementioned external surface is then provided on the jacket and the power train is provided (i.e., it is effective) between the core and the jacket. The damping means can be arranged to damp axial vibrations between the core and the jacket.
The damping means can comprise first and second dampers which are respectively disposed at the first and second end portions of the piston, and at least one of the dampers is or can be confined in the jacket.
The core can be installed for movement relative to the jacket, or vice versa, in the axial direction of the housing, and such master cylinder can further comprise a friction generating device which is arranged to oppose axial movements of the jacket and the core relative to each other.
The means for damping vibrations can include the outer side of the core and the inner side of the jacket of the piston. Such inner and outer sides contact each other.
The core of the piston can comprise a plurality of sections which are movable relative to each other within the jacket, and the damping means can comprise means for biasing the sections of the core against the jacket. For example, the core can comprise two sections which are mirror images of each other, and the means for biasing the two sections away from each other can comprise at least one resilient element which is interposed between the two sections.
The core of the piston can form part of the damping means, and such core can constitute a shock absorber of the damping means.
The piston can be made of one piece, and such one-piece piston can be made of a metallic material.
The one end portion of the piston can be provided with a recess, and the damping means can comprise a damper which overlies the recess and is in contact with the piston rod. Such damping means can further comprise a supply of hydraulic fluid in the recess.
The piston can comprise a hollow cylindrical body which defines a compartment, and the damping means can comprise a supply of damping fluid in the compartment and a damper provided in the hollow body of the piston; such damper seals the compartment and is in contact with the piston rod. Such compartment can have one of its ends sealed by the damper and its other end sealed by a jacket which forms part of the piston. The jacket or the body of such piston can include a shoulder which abuts the damper. If the shoulder is provided on the body of the piston, the latter can further comprise a distancing element which is disposed in the body between the damper and a portion of the jacket. The distancing element can comprise a sleeve having one end portion abutting the damper and another end portion abutting the aforementioned portion of the jacket.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved master cylinder itself, both as to its construction and the modes of assembling, installing and operating the same, together with numerous additional important features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.